Graves’ ophthalmopathy (GO), also known as thyroid eye disease or Graves’ orbitopathy, is an autoimmune inflammatory disorder of the orbit, commonly associated with Graves’ disease, which in severe cases may lead to proptosis, diplopia, and even vision loss. While corticosteroids and surgical interventions have long been the mainstays of treatment, radiotherapy (RT) has emerged as a valuable adjunct, particularly in moderate-to-severe or steroid-refractory cases. RT exerts anti-inflammatory and immunomodulatory effects, contributing to the reduction of orbital edema, extraocular muscle involvement, and compressive symptoms. Evidence-based studies demonstrate that orbital RT yields significant improvements in clinical outcomes, especially in reducing ocular muscle involvement and diplopia, with response rates around 50–80% in appropriately selected patients. Although concerns about radiation-induced toxicity to critical ocular structures—such as the lens and retina—have persisted, modern techniques (intensity-modulated radiotherapy, volumetric modulated arc therapy, and proton therapy) enable precise targeting, thereby significantly minimizing such risks. Clinical trials and long-term studies have demonstrated functional improvement, sustained symptomatic relief, and a low complication profile. Despite ongoing debate regarding optimal timing and patient selection, RT remains a well-established modality in the multidisciplinary management of GO. This chapter provides a comprehensive review of the pathogenesis of GO, the rationale and technique of orbital RT, clinical outcomes, toxicity considerations, and emerging directions for future refinement.